1. Field of the Invention
The present invention relates to a ball formation method and ball forming device used in a wire bonding apparatus.
2. Prior Art
A wire bonding apparatus typically includes a step that causes a discharge to occur by way of applying a high voltage between an electric torch and a tip end of a wire that extends out of the lower end of a capillary, thus forming a ball at the tip end of the wire.
Japanese Patent Application Laid-Open (Kokai) No. 9-298215, for instance, discloses a ball forming device that performs a stable discharge by way of eliminating unstable elements during ball formation process in order to obtain a constant ball diameter. In this ball forming device, an electric torch is employed; and this electric torch is covered by a cover, that is made of a tubular insulating material, with a gap between the vicinity of the discharge portion of the electric torch and the insulating material. In other words, because of such a gap, there is no boundary between the electric torch and the cover; and as a result, the diameter of the formed balls can be constant.
The above-described prior art, however, merely eliminates the effects on the electric torch caused by the cover that covers the electric torch; and no alleviation of the effect of the atmosphere that surrounds the electric torch is taken into consideration. Though certain effects are recognized in this device, a constant formation of a small ball in particular is not sufficiently satisfied when it comes to ultra-fine-pitch bonding.
Accordingly, the object of the present invention is to provide a ball formation method and a ball forming device used in a wire bonding apparatus, in which the free electrons on the surface of an electric torch are activated, the atmosphere surrounding the electric torch is stabilized, and a stable electric discharge is provided so as to produce constant diameter balls at the end of a wire.
The above object is accomplished by a unique ball formation method of the present invention that is used in a wire bonding apparatus in which a discharge is caused to occur by applying a high voltage between an electric torch and a tip end of a wire that extends out of a lower end of a capillary so as to form a ball at a tip end of the wire; and in the present invention, the discharge is performed in a state in which a discharge portion of the electric torch is covered by an insulating member with a space formed between the discharge portion and the insulating member, and in a state in which the space is being heated by a heating means.
The above object is further accomplished by a unique ball forming device of the present invention that is used in a wire bonding apparatus in which a discharge is caused to occur by applying a high voltage between an electric torch and a tip end of a wire that extends out of a lower end of a capillary so as to form a ball at a tip end of the wire; and in the present invention, the ball forming device is comprised of: an insulating member which covers the electric torch with a space formed between the vicinity of a discharge portion of the electric torch and the insulating member, and a heater provided on the insulating member so as to heat the space.